Recently, much interest has focused on the possibility of parallel optical processing of data by means of large, two-dimensional arrays of active, optical, logic gates. Active, optical devices capable of effecting logical functions such as AND and OR have, in fact been reported. See, for example, W. K. Chart, et at., "Optical AND gates using vertically integrated surface emitting laser-phototransistors," PDP-18, Annual Meeting of the Optical Society of America, 1990, Boston, Mass.; T. Numai, et al., "Surface-emitting laser operation in vertical-to-surface transmission electrophotonic devices with a vertical cavity", Appl. Phys. Lett. 58 (1991) 1250-1252; and G. R. Olbright, et al., "Cascadable laser logic devices: discrete integration of phototransistors with surface-emitting laser diodes", Electron. Lett, 27 (1991) 216-217. However, in the interest of simplicity and versatility, it is advantageous to provide a single logic function which is capable of generating a complete logic family. The AND and OR functions are not complete in that sense.
The NOR logical function does, however, generate a complete logic family. An optical logic device capable of effecting the NOR function has been reported in D. Jie, et al., "Hybrid Optical Bistability and Optical Logic Gates with Avalanche Heterojunction Phototransistor and Semiconductor Laser Diodes", IEEE J. Quantum Electron. QE-23 (1987) 1868-1874. Described in that article is an optical logic gate which relies upon the negative resistance behavior of an avalanche heterojunction phototransistor (AHPT) operated in the avalanche breakdown region. That optical logic gate is an optically bistable device which requires bistable switching. However, bistable modes of operation are: undesirable for at least some applications. Moreover, the AHPT is critically biased because the negative differential resistance region is voltage-sensitive. As a result, such a device is relatively unstable against external power-supply fluctuations. Still further, the phenomenon of "critical slowing down", which has been observed in such hybrid bistable optical devices, is expected to limit the speed of such a device.